Is Black Carbon Underestimated as a Global Warming Agent?

Scripps Institution of Oceanography / University of California, San Diego

Satellites have measured black carbon emissions generated by millions of wood-burning stoves throughout the developing world, but a project taking place in India's Uttar Pradesh province suggests the atmospheric heating effect of these soot emissions are at least twice as large as reported by many IPCC models.

Veerabhadran Ramanathan

Even studies relying on satellite data may be underreporting the soot heating effects, said Veerabhadran Ramanathan, a climate and atmospheric scientist at Scripps Institution of Oceanography, UC San Diego.

At the 2011 AGU Fall Meeting in San Francisco (A14C-01 · Monday, Dec. 5, 4-4:30 p.m. Room 3004), Ramanathan will report on results from the pilot phase of Project Surya, a multi-dimensional endeavor to measure the climatic and social effects of replacing traditional cooking methods with cleaner ones. The province in which the project is taking place lies within the Indo-Gangetic Plains region in northern India where air pollution from urban and rural sources frequently amasses. Project Surya scientists argue that mitigating black carbon emissions from its chief sources can provide immediate benefits in the fight to stop warming from producing profound negative effects on society and the natural world. This benefit would complement improvements in public health afforded by cleaner air and, according to recent studies, likely increases in crop yields.

Satellite aerosol optical depth (AOD) for the period between Oct. 1, 2009 and April 14, 2010, over India shows the increased thickness of air pollution over the Indo-Gangetic Plain in the northeasetern portion of the country.

The researchers will discuss findings regarding four aspects of the Surya pilot phase. In one study, they found that black carbon concentrations at ground level peak during morning and evening cooking hours.

In a second study recently submitted for publication, Project Surya researchers concluded that certain forced-draft cookstoves-ones they intend to substitute for traditional wood- or dung-burning stoves-are capable of reducing black carbon emissions by as much as three or four times.

The Surya team has also recently completed two studies addressing the project's data collection methods. One reported the successful demonstration of a reporting system in which residents at the test site submitted ground-level measurements of ambient black carbon levels using cell phones supplied by the researchers. A second paper currently in review demonstrates that during dry winter months when air pollution remains confined to lower altitudes, Surya researchers will be able to measure from satellites the effects of introducing clean-burning cookstoves. The change in cooking methods is anticipated to create a black carbon "hole" in which diminished aerosol thickness should be measurable from space.